1. Field of the Invention
The present invention relates to a terminal pressure welding device and a method for pressure welding a terminal onto electric wires. This improved pressure welding device can pressure weld a terminal simultaneously onto two thick wires as desired, and make the pressure welding widths of terminals as uniform as possible so that the terminals can surely be inserted into the terminal receiving chambers of a connector.
2. Related Art
FIG. 8 illustrates a conventional connector. A connector housing 1 is provided with a plurality of terminal receiving chambers 2. Each of the terminal receiving chambers 2 accommodates a terminal 4 which is pressure welded onto the edge of a wire 3 and held by a flexible stopper arm (not shown) inside the chamber. However, a terminal 4' pressure welded onto the edges of two wires 3 and 3' (double pressure welding) may be inserted into each terminal receiving chamber 2 in the case of branch connection, and the like.
The terminal 4 comprises an electric contact 4A for a mating terminal (not shown), and a wire pressure welding portion 4B. The wire pressure welding portion 4B is provided with a pair of wire barrels 5 for the conductor 3a of the wire 3, and a pair of insulator barrels 6 for an insulating cover layer 3b.
The terminal 4' for double pressure welding has substantially the same structure as that of the terminal 4, but a pair of wire barrels 5' and a pair of insulator barrels 6' of a wire pressure welding portion 4B' are made a little longer than the barrels 5 and 6 of each terminal 4 connected to only one wire 3.
The positions of the two wires 3 and 3' to be pushed into the pair of insulator barrels 6' can be categorized roughly into the following four types: (A) a vertical arrangement; (B) a left-inclined arrangement; (C) a right-inclined arrangement; and (D) a horizontal arrangement.
FIG. 10 illustrates a conventional double pressure welding device which comprises a crimper 7, an anvil for placing the terminal 4', and a wire holding member 9. The wire holding member 9 descends right behind the wire pressure welding member 4B' (i.e., in an axially spaced position) to push the pair of wires 3 and 3' into a space between the pair of insulator barrels 6' by the horizontal holding surface 9a. After that, the crimper 7 descends to caulk the barrels 6' by covering the wires 3 and 3' with them.
At the bottom of the crimper 7, as shown in FIG. 11, a shallow caulking groove 7b is formed on one side of the center (on the left side in the figure) extending from an introducing groove 7a which becomes wider at the opening end, while a deep caulking groove 7c is asymmetrically formed on the other side (on the right side in the figure). The grooves 7b and 7c are connected via an inclined surface 7d.
When actually performing double pressure welding, the pair of wires 3 and 3' in the vertical arrangement shown in FIG. 9A are placed between the insulator barrels 6.sub.1 ' and 6.sub.2 ', and they remain in the vertical arrangement, since the wire holding member 9 descends vertically. If the diameter of the wires is large, the arranged height of the wires 3 and 3' becomes higher than the edge 6a' of the insulator barrel 6.sub.1 ' on the side of the shallow caulking groove 7b, as shown in FIG. 11.
If the crimper 7 descends in such condition, the edge 6a' of the insulator barrel 6.sub.1 ' cannot be placed below the other insulator barrel 6.sub.2 ', and the edge 6b' of the insulator barrel 6.sub.2 ' cannot be interposed between the insulator barrel 6.sub.1 ' and the caulking groove 7b. This causes the edges 6a' and 6b' to collide with each other. As a result, the entire shape becomes somewhat flat, and the insulator barrel 6.sub.2 ' on the right side is buckled in the middle, as shown in FIG. 12. In such pressure welding condition, there is a problem that, since the pressure welding width of the terminal becomes large, the terminal 4' cannot be inserted into the terminal receiving chamber 2 shown in FIG. 8.
Even if the terminal is successfully inserted, the buckled portion will be cracked, and the pressure welding strength is low. When the wires are pulled, the tensile strength will act directly on the wire barrels 5', which might result in cutoff due to vibration.